The invention relates generally to desalination systems and methods for pure water production. More particularly, this invention relates to desalination systems and methods using ion exchange membranes for removal of hardness ions for high purity water production.
Water with high purity are widely used in in many industrial processes, such as in high-pressure boilers in power plants, production of semiconductor elements, production of printed circuit boards, production of integrated circuit, and production of injection water for medical purpose.
Typically, due to continuous operation, and stable and relatively higher quality of product water, electrodeionization (EDI) apparatuses have been employed for processing such liquid steams, for example for production of pure water. Generally, the EDI apparatuses use conventional electrodialysis systems with ion exchange resin filled therein to process the liquid streams. However, during operation, because polyvalent cations with higher concentration may cause scaling tendency, the EDI apparatuses have a hardness tolerance for the liquid streams to be processed. For example, the hardness tolerance of the EDI apparatuses is about less than 1 ppm, which may need rigorous pretreatment of the liquid streams to decrease the hardness therein before the liquid streams are introduced into the EDI apparatus.
There have been attempts to pretreat the liquid streams to decrease the hardness therein. For example, reversal osmosis (RO) apparatuses are employed. However, the processing efficiency of the reversal osmosis apparatuses may be relatively lower for decreasing the hardness in the liquid streams to a certain level suitable for the EDI apparatuses. As a result, the processing cost may be increased accordingly.
Therefore, there is a need for new and improved desalination system and method for removal of hardness ions for high purity water production.